The present invention relates to the general field of housings made of metal extruded section members and designed for manufacturing waterproof power electronic devices.
Such waterproof power devices are, for example, battery chargers designed to be installed on board vehicles such as, for example, fork-lift trucks, golf carts, etc. that can be cleaned using methods that are relatively intrusive, such as, for example, methods using high-pressure fluid. In such applications, it is necessary for the battery charger to be fully waterproof in order to protect the electronic components that it contains.
In the particular context described above, it is naturally out of the question to use conventional ventilation with a fan blowing air into the housing. The action of the fan requires an opening to be provided, and fluid or solid particles can enter the housing through the opening, which is unacceptable for this type of power electronic device.
More particularly, the invention relates to such a housing whose extruded section member forms a tunnel that is of substantially rectangular closed section and that is provided with fins on at least one side of the rectangle. By increasing the heat exchange area via which the housing can exchange heat with the outside air, the fins make it possible to dissipate heat. The heat dissipation is increased when a flow of air is blown in contact with the fins. However, in the particular context described above, it is also out of the question to position a fan for blowing air over the fins of the housing. That is because fan technology does not make it possible to implement such a fan with satisfactory and relatable waterproofness at a reasonable cost.
Generally, a side that is not provided with fins serves as a base for fastening the housing and as a support for supporting the power electronic components of the power electronic device.
The housing can then exchange heat to a marginal extent with the support to which it is fastened. However, the nature of said support is totally unknown a priori. Its material, its thickness, or its surface can have very varied thermal characteristics allowing heat to be removed or preventing heat from being removed.
Thus, since the housing is closed and cannot be ventilated externally, it must therefore exchange the heat it generates with the surrounding air solely via radiation and natural convection, i.e. without artificial ventilation.
Even more precisely, the fins of the extruded section member forming the housing are thus adapted to the situation in which air flows by natural convection in the extrusion direction outside the housing.
Therefore, it is necessary to make provision for natural convection and for radiation to be maximized in order to guarantee that sufficient heat is removed to enable the power electronic device placed inside the housing to operate properly.
In addition, it is known that power electronic devices are generally mass-produced and are subject to very tight cost constraints.
As regards satisfying cost constraints and procuring waterproofness, it is known that the use of a one-piece element extruded to form a tunnel is particularly advantageous because it guarantees waterproofness on all four sides of the housing. This also facilitates mounting the battery charger or, more generally, mounting a power device, and thus contributes to reducing the final cost of the power electronic device.
For a heat dissipater or “heatsink”, extruding an aluminum tunnel requires the fins to be in the extrusion direction. Therefore, currently existing housings made of extruded section members are provided with fins in the extrusion direction, and they thus enable the heat generated inside the housing by the power electronic device to be removed via the fins, provided that said fins are positioned in such a manner as to be vertical.
It is also known that thermal performance improves not only with increasing surface area in contact with the air, hence the advantageousness of fins, but also with increasing speed of air over said surface area. The air heating on coming into contact with the fins generates a natural upward movement of air, which movement is facilitated if the air can rise freely, and thus if the fins extend vertically.
Mounting the housing on a vertical wall with the fins also extending vertically thus procures optimum dissipation for an extruded housing. This requires the power device to be installed in the same way in all vehicles in which the power electronic device is to be installed.
Currently, this is a constraint that is holding back the development of the use of power devices implemented using extruded housings. A very wide variety of contexts are thus currently deprived of this solution.
Unfortunately, if the device is mounted on a horizontal plane, the plane of the fins is then also horizontal, and the convection of air is much weaker. In spite of the existence of radiation, a very significant reduction in effectiveness (a reduction by more than 30%) is observed.
Therefore, assembled solutions exist in which radiators carrying fins are assembled on a pre-extruded tunnel that is not provided with fins. That makes it possible for the direction of the fins to be perpendicular to the extrusion direction or for the direction of the fins to form an angle with said extrusion direction. The radiators used have standard comb-shaped section members that generally have long fins mounted on thick bases and that are designed for forced convection. Forced convection requires a higher density for the heat flow and thus greater thickness for the base of the fins. Such solutions generally lead to housings having a very large mass of aluminum or of metal, which is penalizing. In addition, such solutions are complex to manufacture in terms of machining and of assembly, because the waterproofness constraint is still present.